1. Field of the Invention
The present invention relates to a control system for an automotive air conditioning unit. More particularly, the present invention relates to a control system which acts to disengage an air conditioner from the power train of a vehicle when engine power is needed for other uses such as, accelerating, travelling uphill, and towing heavy payloads.
2. Description of the Prior Art
In all motorized vehicles with air conditioning systems, the power available, for example for acceleration and traveling uphill, is reduced when the air conditioning system is turned on. With the increase in consumer demand for cars with greater fuel economy, there has been a great rise in the popularity of cars with smaller engines, in particular cars with small four cylinder engines. Such small engines have more limited power outputs than, for example, the large eight cylinder engines popular in the recent past.
Because of the limited power of such small engines, it is often impossible, in cars with such engines, to accelerate quickly or to travel uphill at a reasonable speed, with the air conditioner on. Also, in the case of police vehicles for example, when the quickest possible acceleration is required, it is desirable to direct all available power to the drive wheels without the need for the vehicle operator's intervention. For these reasons, many systems have been proposed in the prior art for automatically turning off a vehicle's air conditioner when the demand for engine power is high.
U.S. Pat. No. 5,271,368, issued to Fujii et al., shows a fuel supply control system which cuts off fuel supply to the engine during deceleration when the engine speed is higher than a first preset value with the air conditioner on, and when the engine speed is higher than a second preset value with the air conditioner off, the first preset value being greater than the second preset value.
U.S. Pat. No. 5,261,368, issued to Umemoto, shows an engine control system for preventing engine stall when the engine returns from operating under a load to an idling condition. The Umemoto system supplies auxiliary air to the engine, to prevent the engine speed from dropping below the idle setting in the period of time immediately following the return of the throttle valve to the idling position.
U.S. Pat. No. 5,133,302, issued to Yamada et al., shows a control system, for controlling the cooling fan of an engine, which uses the vehicle speed, coolant temperature, and refrigerant pressure at the compressor discharge outlet, to determine whether the cooling fan should be on or off.
U.S. Pat. No. 5,050,395, issued to Berger, shows a an air conditioning shutoff system that uses the difference between fuel consumption per stroke at idle and actual fuel consumption per stroke, as the criterion for shutting off the vehicle's air conditioner. In addition, the Berger system uses engine RPM, vehicle speed, and accelerator pedal position, as further parameters for determining when to shutoff the air conditioner. All the aforementioned additional parameters have preset thresholds, and the air conditioner is not shutoff if the value for any one of these parameters is above its preset threshold.
U.S. Pat. No. 5,027,609, issued to Yashiki et al., shows an air conditioning shutoff system where the air conditioner is shutoff when the intake pressure is above a certain threshold. In the Yashiki et al. system, the intake pressure threshold is dynamically varied depending on engine RPM and ambient pressure.
U.S. Pat. No. 4,823,555, issued to Ohkumo, shows an air conditioner shutoff system which compares the actual engine intake pressure to a reference pressure which is a function of the vehicle's speed, and shuts off the air conditioner if the intake pressure is higher than the reference pressure at a particular vehicle speed.
U.S. Pat. No. 4,688,530, issued to Nishikawa et al., shows an air conditioning shutoff system which operates to shutoff the air conditioner compressor when the vehicle is in a low speed range and the throttle opening is less than a reference amount. The purpose of this control system is to eliminate engine vibrations when the vehicle's automatic transmission down-shifts at low speed, with the air conditioner running.
U.S. Pat. No. 4,658,943, issued to Nishikawa et al., shows an air conditioner shutoff system which uses the data from the electronic controller of the vehicle's automatic transmission to determine whether the throttle opening and the vehicle speed are within a "prohibition region" within the shift map stored in the transmission controller. If the values for the vehicle speed and throttle opening are within the "prohibition region" and certain other requirements, regarding the selected gear and the elapsed time kept by a timer are met, then the air conditioner is shutoff. Also the air conditioner is shutoff if the engine speed in rpm is below a reference value.
U.S. Pat. No. 4,615,180, issued to Rudman, shows an inertial mercury switch which tilts in response to vehicle acceleration, and causes an open circuit when tilted. By incorporating this switch in the circuit supplying power to the air conditioner compressor clutch, the air conditioner compressor can be cut out during vehicle acceleration, thereby making more engine power available for acceleration. The Rudman system fails to cut out the air conditioner when towing a heavy load at constant speed, a condition which also requires greater engine power output.
U.S. Pat. No. 4,610,146, issued to Tanemura, shows a an air conditioning shutoff system that uses fuel temperature to determine when the engine is running under a heavy load. In addition, the Tanemura system incorporates a detector for detecting the amount of accelerator pedal depression, and a speed sensor. When the fuel temperature is higher than a certain level, the accelerator pedal is depressed further than a preset amount, and the vehicle speed is below a preset level, the system of Tanemura acts to shutoff the air conditioner compressor.
U.S. Pat. No. 4,510,764, issued to Suzuki, discloses an air conditioning cut-off where during acceleration or high load operation the power supplied to the air conditioner is reduced or eliminated. Suzuki uses the intake pressure of the engine to detect high load operation. Suzuki does not disclose how his system determines whether or not the vehicle is accelerating.
U.S. Pat. No. 4,488,410, issued to Seiderman, shows an air conditioner cut-off system which uses an on-off switch, actuated by the gear shift lever, to turn off the air conditioner while the transmission is being shifted between neutral and high gear. Presumably, as the transmission is being shifted through the low gears, demand for engine power is high and the air conditioner should be turned off.
U.S. Pat. No. 4,445,341, issued to Hayashi, shows an air conditioner cut-off which uses the engine air intake vacuum to determine whether or not the vehicle is under acceleration and, in response to a determination that the vehicle is accelerating, turns off the air conditioner.
U.S. Pat. No. 4,369,634, issued to Ratto, shows another example of an air conditioner cut-off which uses the engine air intake vacuum to determine whether or not there is a demand for high engine power, and turns off the air conditioner when there is a demand for high engine power.
U.S. Pat. No. 4,359,875, issued to Ohtani, shows an air conditioning cut-off which uses engine intake vacuum to determine when the vehicle is in a condition other than standing still or travelling at constant velocity. The air conditioner is then turned off when the intake manifold pressure is greater than -150 mmHg.
U.S. Pat. No. 4,305,360, issued to Meyer et al., shows a control system for automatically setting the idle speed of the engine. The Meyer et al. system automatically opens the throttle valve, when the engine speed drops below the idle speed setting, to a position which brings the engine speed up to the idle speed setting.
U.S. Pat. No. 4,299,094, issued to Lummen, shows an air conditioner cut-off system which uses a mercury switch to turn the air conditioner on and off. Again the mercury switch is responsive to engine intake vacuum.
U.S. Pat. No. 4,269,033, issued to Birch, shows a pressure sensitive switch for turning off the air conditioner in response to high intake manifold pressure. The pressure sensitive switch of Birch has an adjustment screw which allows the degree of vacuum, which causes the air conditioner to be turned off, to be set by the vehicle operator.
U.S. Pat. No. 4,237,838, issued to Kinugawa et al., shows an engine control system that regulates the amount of air flowing into the engines intake manifold.
U.S. Pat. No. 4,135,368, issued to Mohr et al., shows an air conditioner cut-off which turns off the air conditioner in response to high engine intake pressure, and turns on the air conditioner after a pre-programmed time of three to seven seconds.
U.S. Pat. No. 3,462,964, issued to Haroldson, shows a pressure sensitive switch for turning off the air conditioner in response to high intake manifold pressure.
Japanese Patent Document Number 55-151135 shows a control system for controlling the supply of auxiliary air to the intake manifold of an engine.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.